1. Field of the Invention
The present invention relates to an apparatus for inspecting characteristics of a semiconductor device employed for inspecting electrical characteristics of the semiconductor device.
2. Description of the Related Art
In a conventional method, manual inspection by an inspector is done by pushing probe pins on to an inspection point onto the semiconductor chip while inspecting the semiconductor device or semiconductor chip. The conventional inspection method will be described in conjunction with the drawings in FIG. 5 through FIG. 10.
FIG. 5 is a perspective view illustrating a conventional manual inspection method for inspecting electrical characteristics of semiconductor chips. FIG. 6 is a perspective view illustrating a semiconductor chip on which a radiating plate is soldered. FIG. 7 is a sectional view of a contact probe pin of the conventional inspection method. FIG. 8 is a sectional view of a soldering fixture used for soldering the radiating plate of the semiconductor chip according to the prior art. FIG. 9 is a perspective view of a lower fixture for soldering employed for soldering the radiating plate on the semiconductor chip. FIG. 10 is an electrical circuit diagram of a power transistor chip.
As shown in FIG. 6, the semiconductor chip 1 is configured by soldering a wafer chip 3 on the radiating plate 2 with solder 4. As shown in FIG. 5, many semiconductor chips 1 waiting for inspection of electrical characteristics are transferred in a metallic tray 5 which accommodates semiconductor chips 1 during the inspection period. The metallic tray 5 is connected to a tester 8 for inspecting electrical characteristics via a tester cable 7 with a crocodile clip 6. As shown in FIG. 7, a contact probe pin 11 is mounted on the tip of a contacting fixture connected to the tester 8 through a tester cable 10. The contact probe pin 11 has a structural such that a contacting pin 11a passes through the contact sleeve 11b, freely sliding within the sleeve 11b, and resiliently loaded in the contact sleeve by a spring 11c with the pin 11a protruding from the contact sleeve 11b.
As shown in FIGS. 7 and 8, a soldering fixture 12 is used for soldering the radiating plate 2 on the semiconductor wafer chip 3. The soldering fixture 12 comprises a lower fixture 13 for positioning and supporting the radiating plate 2, a middle fixture 14 for positioning the wafer chip 3 fixedly on the lower fixture 13, and a pressing fixture 15 mounted on the middle fixture 14. The lower fixture 13 includes spot facing holes 13a to fit and hold the radiating plate 2, recesses 13b for hydrogen ambient ventilation, and positioning holes 13c in which positioning pins 14a vertically mounted in the middle fixture 14 fit. As indicated in FIG. 9, the spot facing holes 13a are arranged in double or two rows. The solder 4 is melted and fixed in advance on the radiating plate 2 placed in the lower fixture 13. To melt and fix the solder 4, the radiating plate 2, on which the unmelted solder 4 is placed and overlaid, is put into a hydrogen oven. The middle fixture 14 has through holes 14b for positioning wafer chips at a position corresponding to spot facing holes 13a of the lower fixture 13. The pressing fixture 15 has weights 15a for applying pressure to each chip 1 to urge the wafer chip 3 against the solder 4 on the radiating plate 2.
The following is a description of an inspection method of a conventional semiconductor chip.
The radiating plate 2 is soldered on the wafer chip 3 before the inspection process, In the soldering operation, firstly, the radiating plate 2 on which the preliminary solder 4 is melted and fixed in advance is placed in the lower fixture 13 of the wafer-chip soldering fixture 12. At this time the solder 4 faces upwardly. Secondly, the middle fixture 14, having positioning pins 14a which are inserted in positioning holes 13c of the lower fixture 13, is overlaid on the lower fixture 13. Then, the wafer chip 3 is inserted in the through hole 14b of the middle fixture 14, and finally the pressing fixture 15 having weights 15a for applying pressure to each chip 1 is overlaid on top of that. After the completion of the soldering preparation, the soldering fixture 12 is put into the hydrogen ambient atmospheric oven where the temperature is controlled to satisfactorily melt the solder, thus bonding the radiating plate 2 to the wafer chip 3. After completing the soldering, the pressing fixture 15 and the middle fixture 14 of the soldering fixture 12 are removed at the exit of the hydrogen ambient atmospheric oven. Then each semiconductor chip 1 is cooled in the lower fixture 13, and transferred to the inspection process.
In the inspection process, the semiconductor chip 1 is transferred from the lower fixture 13 to the metallic tray 5 by means of a pair of vacuum tweezers (not shown in FIGs.), and then the tester cable 7 of the tester 8 is connected to the metallic tray 5 by means of the crocodile clip 6. In the same manner, a measurement circuit for inspecting characteristics of the semiconductor chips 1 is formed by pressing the contacting fixtures 9, which are connected to the tester 8 through tester cables 10, on a specific point (inspection point) on the upper surface of the wafer chip 3. When the contacting fixture 9 is pressed against the surface of the wafer chip 3, the compression spring 11c incorporated in the contact probe pin 11 flexes and an appropriate contacting pressure is applied to the contacting pin 11a. Then, a foot switch (not shown in FIGs.) under the inspection work table is operated to send a start command signal to the tester unit, and the inspection by the tester 8 can be carried out. The testing result is displayed on the front panel display (not shown in FIGs.), and an inspector sorts defective products. When there are a plurality of inspection points in one chip, the contacting fixture 9 should be moved in turn, and the same inspection procedure repeated. Conventionally, the inspection of characteristics of the semiconductor chip 1 has been made as described above. In the conventional inspection method, all the inspection-related works, such as transferring the finally assembled semiconductor chips 1 from the soldering fixture 12 to the metallic tray 5; inspecting; and sorting of good and defective products and transferring them to molded trays, has been done manually requiring enormous labor.
Furthermore, in the conventional method, as illustrated in FIG. 5, the semiconductor chip having a plurality of inspecting points allows the inspection of single transistor cells which is not practical. In addition, there is a problem in obtaining a correlation between characteristics of single chip units and operation in a mode when all the units are actuated. Therefore, an accurate and reliable classification of chips has been impossible.
Furthermore, as the contacting pressure of the contact probe pin 11 varies according to the hand pressure applied by inspectors, problems used to occur such as an instability in the measurement accuracy caused by contact failure and breakage of the chip caused by inaccurate positioning of the contact point during the inspection.
In addition, with regard to assembling accuracy of the wafer chip 3 against the outer shape of the radiating plate 2 after the solder bonding of these two members, there is a chance of inaccurate positioning of the wafer chip 3 by an extent of the clearance between the fixture and the work. Accordingly, in manner of positioning based on the reference to the outer shape of the radiating plate 2, there has been difficulty in modifying the fixture so that it enables contacting simultaneously a plurality of inspection points on one chip.